A variety of supplemental recovery techniques have been employed in order to increase the recovery of viscous oil from subterranean viscous oil-containing formations. These techniques include thermal recovery methods, waterflooding and miscible flooding.
Heterogeneous hydrocarbon containing subterranean formations, i.e., formations having relatively high permeability zones and relatively lesser permeability zones, are difficult to efficiently flood by secondary and/or tertiary oil recovery processes because fluids preferentially migrate into the highly permeable zones in the subterranean formations. This process is aggravated by natural or accidental fracturing of the formation adjacent the injection well since such fractures commonly occur only in one or a few of the layers in layered formations. The migration described above is undesirable when injecting treatment fluids into oil-containing formations for the recovery of oil since the treatment fluids channel through the highly permeable and/or fractured zones bypassing the less permeable zones. The result is poor conformance and flow profiles of the treatment fluid in the formation. The hydrocarbons residing in the less permeable zones are not produced and the overall yield of hydrocarbons from the formation is reduced.
To increase the efficiency of formation flooding processes, the highly permeable and/or fractured zones in subterranean formations are plugged or partially plugged to prevent or educe migration of treatment fluids into them and to divert treatment fluids into adjacent, less permeable zones. In injection profile control projects, polymeric materials have been used in liquid slurries or suspensions to effectively enter and plug or partially plug the highly permeable and/or fractured zones of the formation. Fluids injected after such a treatment therefore move into unswept areas or zones of the reservoir which results in increased oil recovery.
Accordingly, it is a primary object of this invention to provide a process for improving oil recovery from a subterranean, oil-containing formation comprising first injecting a plugging agent that is stable at very high temperatures and which is very cheap in comparison to polymers into the formation that preferentially enters the highly permeable and/or fractured zones of the formation and plugs the face of said zones, continuing injection of the plugging agent or in the alternative a displacing fluid to form new fractures and/or extensions of existing fractures in the formation and injecting a displacing fluid into the formation at a pressure sufficient to maintain the new fractures and/or extensions of existing fractures open and displace oil from zones communicating with the new fractures and/or extensions of existing fractures toward a production well where it is recovered. Formation of the new fractures and/or extensions of existing fractures enables additional oil-containing zones in the formation to be penetrated by the displacing fluid for the recovery of oil thereby improving oil recovery from the formation.